This invention relates to heat engines, and is more particularly related to an open-cycle heat engine in which steam is employed as a source of heat. The invention is more specifically concerned with a thermodynamic process employing air and water vapor as the working fluid, which expands and cools to produce work and exhausts from the system at a temperature below the earth's average ambient temperature.
All matter contains energy in the form of heat energy or enthalpy. This energy flows in one direction only, that is, from material at high temperature to material at low temperature. The flow of energy is heat, and can be compared with fluids, such as water, which flows to produce work. In the case of water, potential energy in the form of elevated water is converted to kinetic energy in the form of flowing water. Some of this kinetic energy is converted to useful energy, i.e., work, by an engine such as a water turbine. The rest of the kinetic energy is discarded as waste. In the case of a hot material, which stores energy, i.e., enthalpy, and this energy is converted to kinetic energy by permitting the material, i.e., a gas, to expand and flow. Some of this kinetic energy can be converted to useful work, e.g., in a gas turbine. The remainder of the kinetic energy is discarded as waste heat, and ultimately winds up in the atmosphere.
Every heat engine requires a working medium, which can typically be steam or another working gas. In modem engines, this working medium is usually gaseous or vaporous in form, with the preferred choice being steam. Early steam engines had an energy conversion efficiency of less than 5%, and discarded 95% of their initial energy as waste heat to the atmosphere. By the development of improved engines, including the development of the Rankine Cycle, and with the addition of condensers and water pumps, conversion efficiency was increased to 20% and above. More recently, turbine design improvements, such as feed water heating, higher operating temperatures, superheating, reheat cycles, etc., have further increased conversion efficiency to exceed 35%. However, improvements much above this efficiency level have been elusive in the heat engine arts.